Hydrogen is widely believed to be the world's next generation fuel, since its oxidation does not emit greenhouse gases that contribute to climate change. Auto manufacturers are investing significantly in hydrogen vehicles. Other transportation vehicles, such as ships, trains and utility vehicles also represent promising opportunities for use of hydrogen fuel. Thus there is need for a reliable, safe, efficient and economic process for the production of hydrogen gas for fuel.
Electrolysis is a proven, commercial technology that separates water into hydrogen and oxygen using electricity. Net electrolysis efficiencies are typically about 24%. In contrast, thermochemical reactions to produce hydrogen using nuclear heat can achieve heat-to-hydrogen efficiencies up to about 50% [See Schultz, K., Herring, S., Lewis M., Summers, W., “The Hydrogen Reaction”, Nuclear Engineering International, vol. 50, pp. 10-19, 2005 and Rosen, M. A., “Thermodynamic Comparison of Hydrogen Production Processes”, International Journal of Hydrogen Energy, vol. 21, no. 5, pp. 349-365, 1996.]
A copper-chlorine (Cu—Cl) cycle has been identified by Atomic Energy of Canada Ltd. (AECL) [See Sadhankar, R. R., Li, J, Li, H., Ryland, D. K., Suppiah, S. “Future Hydrogen Production Using Nuclear Reactors”, Engineering Institute of Canada—Climate Change Technology Conference, Ottawa, May, 2006 and Sadhankar, R. R., “Leveraging Nuclear Research to Support Hydrogen Economy”, 2nd Green Energy Conference, Oshawa, June, 2006.] at its Chalk River Laboratories (CRL) as a highly promising cycle thermochemical for hydrogen production. Water is decomposed into hydrogen and oxygen through intermediate Cu—Cl compounds. Past studies at Argonne National Laboratory (ANL) have developed enabling technologies for the Cu—Cl thermochemical cycle, through an International Nuclear Energy Research Initiative (I-NERI), as reported by Lewis et al. [See 17. Lewis, M. A., Serban, M., Basco, J. K, “Hydrogen Production at <550° C. Using a Low Temperature Thermochemical Cycle”, ANS/ENS Exposition, New Orleans, November, 2003.] The Cu—Cl cycle is well matched to Canada's nuclear reactors, since its heat requirement for high temperatures is adaptable to the Super-Critical Water Reactor (SCWR), which is being considered as Canada's Generation IV nuclear reactor.
Other countries (Japan, U.S. and France) are currently advancing nuclear technology for thermochemical hydrogen production [See Sakurai, M., Nakajima, H., Amir, R., Onuki, K., Shimizu, S., “Experimental Study on Side-Reaction Occurrence Condition in the Iodine-Sulfur Thermochemical Hydrogen Production Process”, International Journal of Hydrogen Energy, vol. 23, pp. 613-619, 2000; Schultz, K., “Thermochemical Production of Hydrogen from Solar and Nuclear Energy”, Technical Report for the Stanford Global Climate and Energy Project, General Atomics, San Diego, Calif., 2003; and Doctor, R. D., Matonis, D. T., Wade, D. C., “Hydrogen Generation Using a Calcium-Bromine Thermochemical Water-splitting Cycle”, Paper ANL/ES/CP-111623, OECD 2nd Information Exchange Meeting on Nuclear Production of Hydrogen, Argonne, Ill., Oct. 2-3, 2003.]
The Sandia National Laboratory in the U.S. and CEA in France are developing a hydrogen pilot plant with a sulphur-iodine (S—I) cycle [See Pickard, P., Gelbard, F., Andazola, J., Naranjo, G., Besenbruch, G., Russ, B., Brown, L., Buckingham, R., Henderson, D., “Sulfur-Iodine Thermochemical Cycle”, DOE Hydrogen Production Report, U.S. Department of Energy, Washington, D.C., 2005 Fuel Cell Vehicles: Race to a New Automotive Future, Office of Technology Policy, US Department of Commerce, January, 2003.] The Korean KAERI Institute is collaborating with China to produce hydrogen with their HTR-10 reactor. The Japan Atomic Energy Agency (JAEA) aims to complete a large S—I plant to produce 60,000 m3/hr of hydrogen by 2020, which will be sufficient for about 1 million fuel cell vehicles [See Suppiah, S., Li, J., Sadhankar, R., Kutchcoskie, K. J., Lewis, M., “Study of Hybrid Cu—Cl Cycle for Nuclear Hydrogen Production”, Third Information Exchange Meeting on the Nuclear Production of Hydrogen, Orai, Japan, October, 2005.] Several countries, participating in the Generation Iv International Forum plan to develop the technologies for co-generation of hydrogen by high-temperature thermochemical cycles and electrolysis, through multilateral collaborations [See Rosen, M. A., “Thermodynamic Analysis of Hydrogen Production by Thermochemical Water Decomposition using the Ispra Mark-10 Cycle”, In Hydrogen Energy Prog. VIII: Proc. 8th World Hydrogen Energy Conference, ed. T. N. Veziroglu and P. K. Takahashi, Pergamon, Toronto, pp. 701-710, 1990.]
When compared to other methods of hydrogen production, the thermochemical Cu—Cl cycle has its own unique advantages, challenges, risks and limitations. Technical challenges include the transport of solids and electrochemical processes of copper electrowinning, which are not needed by other cycles such as the sulfur-iodine cycle. These processes are challenging due to solids injection/removal, which can block equipment operation and generate undesirable side reactions in downstream chemical reactors. Flow of solid materials can lead to increased maintenance costs, due to wear and increased downtime arising from blockage and unscheduled equipment failure. A technological risk involves the potential use of expensive new materials of construction that are needed to prevent corrosion of equipment surfaces. These include surfaces exposed to molten CuCl, spray drying of aqueous CuCl2 and high-temperature HCl and 02 gases. Additional operational challenges entail the steps of chemical separation (which increases complexity and costs) and phase separation (particles, gas, and liquids must be separated from each other in fluid streams leaving the reactors). As a result, the overall cycle efficiency becomes a limitation, wherein the Cu—Cl cycle must compete economically against other existing technologies of hydrogen production.
Despite these challenges and risks, the Cu—Cl cycle offers a number of key advantages over other cycles of thermo-chemical hydrogen production. The attractions include lower temperatures compared to other cycles like the S—I cycle. Heat input at temperatures less than 530° C. make it suitable for coupling to Canada's SCWR (Super-Critical Water Reactor; Generation IV nuclear reactor) and reduced demands on materials of construction. Other advantages are inexpensive raw materials and reactions that proceed nearly to completion without significant side reactions. Solids handling is required, but it is relatively minimal and it can be reduced by combining thermochemical and electrochemical steps together. Another key advantage is the cycle's ability to utilize low-grade waste heat from power plants, for various thermal processes within the cycle. However, before these advantages can be realized, further equipment scale-up is needed.